“The role of plasmids in driving Vibrio harveyi virulence in barramundi (Lates calcarifer) (6891)”

The role of plasmids in driving Vibrio harveyi virulence in barramundi (Lates calcarifer)

Introduction:

Vibrio species are a major animal and public health risk in marine and estuarine environments worldwide and their prevalence is expected to increase with climate change. For tropical and warmwater aquaculture, the opportunist Vibrio harveyi is a major disease risk for regions including the Mediterranean, Southeast Asia and Australia. However, understanding of the virulence in V. harveyi is still somewhat restricted by strain-specific variability and complex host-pathogen dynamics. This study aimed to investigate the drivers of V. harveyi virulence holistically by using a combination of genomic investigation, traditional phenotypic techniques and experimental challenge trials in juvenille barramundi (Lates calcarfier).

Methods:

Twelve V. harveyi isolates were collected from moribund marine fish in Australia and Vietnam experiencing disease consistent with vibriosis. All isolates underwent short-read sequencing and eight were selected for long-read sequencing, phenotypic characterisation and experimental challenge. Phenotypic assays included urease function, lipase, phospholipase, caseinase, swarming, haemolysis, gelatinase and biofilm formation were performed at 22°C, 28°C and 34°C to simulate the likely environmental conditions experienced by barramundi and subsequently V. harveyi in production settings. In addition, 28 V. harveyi genomes were downloaded from the NCBI Sequence Read Archive to investigate antimicrobial resistance genes, 49 common and atypical virulence genes of Vibrio species and to construct a global phylogenetic tree of V. harveyi strains.

Results:

Two of the isolates collected in this study (Vh-14 and Vh-15) were highly distinctive both phenotypically and genotypically. These two isolates had relatively low levels of phenotypic activity (including no urease function) yet contained several plasmids not identified in the other isolates. In vivo challenge trials revealed that these isolates were hypervirulent, causing 100% mortality in less than 48 hours. Long-read sequencing identified multiple plasmids within these isolates including a 109,656 bp conjugative plasmid. This plasmid contained a second type III secretion system (T3SS2) originally associated with Yersinia pestis. This T3SS2 was not identified in any of the other isolates or genomes analysed in this study and marks the first report of a T3SS2 in V. harveyi. Type III secretion systems are a potent virulence mechanism in gram-negative bacteria including Vibrio spp. such as V. cholerae and V. parahaemolyticus.

Conclusions:

The emergence of hypervirulent strains with a plasmid-mediated type III secretion system poses a major risk to sustainable aquaculture in Southeast Asia, the Mediterranean and Australia. Functional investigation of the plasmid is critical to mitigate and safeguard aquaculture production from hypervirulent V. harveyi isolates.

1. Sullivan, Roisin, Sydney School of Veterinary Science, Faculty of Science, The University of Sydney, Camden, NSW, Australia, Presenter
2. Becker, Joy, School of Life and Environmental Sciences, Faculty of Science, The University of Sydney, Camden, NSW, Australia, Author
3. Zadoks, Ruth, Sydney School of Veterinary Science, Faculty of Science, The University of Sydney, Camden, NSW, Australia, Author
4. Venturini, Carola, Sydney School of Veterinary Science, Faculty of Science, The University of Sydney, Camden, NSW, AustraliaTY OF SYDNEY, Author
5. Esteves, Ana, Elizabeth Macarthur Agricultural Institute, New South Wales Department of Primary Industries and Environment, Menangle, New Sout, Author
6. Benedict, Suresh, Berrimah Veterinary Laboratory, Department of Agriculture and Fisheries, Northern Territory Government, Berrimah, Northern Terri, Author
7. Fornarino, Dani, Berrimah Veterinary Laboratory, Department of Agriculture and Fisheries, Northern Territory Government, Berrimah, Northern Terri, Author
8. Andrews, Hannah, Berrimah Veterinary Laboratory, Department of Agriculture and Fisheries, Northern Territory Government, Berrimah, Northern Terri, Author
9. Okoh, God’spower, Berrimah Veterinary Laboratory, Department of Agriculture and Fisheries, Northern Territory Government, Berrimah, Northern Terri, Author
10. Bhardwaj, Vidya, Berrimah Veterinary Laboratory, Department of Agriculture and Fisheries, Northern Territory Government, Berrimah, Northern Terri, Author
11. Sistrom, Mark, Berrimah Veterinary Laboratory, Department of Agriculture and Fisheries, Northern Territory Government, Berrimah, Northern Terri, Author
12. Westman, Mark, Elizabeth Macarthur Agricultural Institute, New South Wales Department of Primary Industries and Environment, Menangle, New Sout, Author
13. Nguyen, Phuoc, Faculty of Fisheries, University of Agriculture and Forestry, Hue University, Hue City, Viet Nam, Author
14. Samsing, Francisca, Sydney School of Veterinary Science, Faculty of Science, The University of Sydney, Camden, NSW, Australia, Author